Nitzschia austriaca Hustedt: a characteristic diatom of Hungarian inland saline waters including a morphological comparison with the type material

A detailed scanning electron microscopic investigation was carried out to clarify the taxonomic status of a small sigmoid Nitzschia species, a potential indicator of Central European soda waters. We found this taxon to be one of the dominant epiphytic diatoms collected from sodic bomb crater ponds at Apaj (Hungary). The large population allowed for a morphometric comparison based on frustule ultrastructure with the type material of the most similar species, Nitzschia austriaca Hustedt that was originally described from a soda pan in the region. The results clearly demonstrated an overlap between the Apaj population and the type material of N. austriaca (based on NMDS analysis), therefore we argue that they represent the same taxon. An emended diagnosis of N. austriaca is given. Total suspended solids and total phosphorous proved to be the most important factors predicting the occurrence of the species, with possible interactive effects of conductivity and pH. We then expanded the distribution of the species by revisiting data originating from previous large-scale surveys targeting sodic habitats in Hungary. On the basis of our results, N. austriaca is a characteristic species for Central European soda waters, including the protected astatic soda pans, indicating their typical chemical and physical characteristics.</jats:p

Biogeography and morphology of a poorly known diatom Dorofeyukea rostellata (Hustedt) Kulikovskiy & Kociolek = Biogeografía y morfología de una diatomea poco conocida Dorofeyukea rostellata (Hustedt) Kulikovskiy & Kociolek

Dorofeyukea rostellata is a rare and poorly known representative of Dorofeyukea genus. To date, this taxon has only been recorded only outside of Europe. In two Croatian lakes, we found a diatom in appearance similar to Dorofeyukea rostellata and within corresponding physical and chemical conditions. Due to the uncertain taxonomical position of this taxon, type material of Dorofeyukea rostellata and a closely related species, Navicula grimmeioides, were analysed by means of light and scanning electron microscopy. Upon a detailed investigation, we could clearly distinguish the Croatian population from N. grimmeioides. However, the Croatian population and the type material of D. rostellata differed only in minor characteristics. The most obvious difference is the shape of areolae. Nevertheless, differences between the shapes of the areolae can be caused by the degree of silicification, which often depends on the environmental conditions. Since almost every other characteristic of the Croatian population overlapped with that of the type material of D. rostellata we identified it as D. rostellata. Additionally, scanning electron microscopy analyses also revealed that N. grimmeioides belongs to the genus Dorofeyukea, so its new combination was proposed

Vertical distribution of zooplankton in a shallow peatland pond: the limiting role of dissolved oxygen

We investigated the diel vertical distribution patterns of microcrustacean zooplankton (Cladocera, Copepoda) in a shallow pond (max. depth: 70 cm) of the Öreg-turján peatland (Ócsa, Central Hungary) during three 24-h periods in July (19–20th), August (17–18th) and September (11–12th) 2011. Environmental variables showed remarkable vertical stratification. Oxygen concentration was close to zero in the entire water column from night until sunrise, while the lower strata (from 20 cm below the surface) were close to anoxic during all three diel cycles. It proved to be the main determinant of the vertical distribution of microcrustaceans. Accordingly, the highest proportion of individuals was present in the surface layer. Chlorophyll-a concentration and phytoplankton biomass were inversely distributed compared to zooplankton. Microcrustaceans (mainly Daphnia curvirostris) migrated to the middle layer only in August, which could be explained by a trade-off between food resources, dissolved oxygen (DO) and competition with littoral zooplankters. The diurnal density patterns of microcrustaceans suggested horizontal migration into the aquatic macrophytes during night, which could be a strategy to avoid Chaoborus predation. Our results show that strong vertical gradients of abiotic and biotic factors occur even in such shallow waterbodies. Among them, DO can maintain constant vertical aggregation of zooplankters by limiting their occurrence to the surface layers

Pantocsekiella, a new centric diatom genus based on morphological and genetic studies

International audiencePrevious morphological studies showed that the description of the Cyclotella genus was too general and according to new morphological criteria new genera were established based on both recent and fossil taxa (e.g. Discostella, Handmannia, Puncticulata, Tertiarius). Furthermore, previous molecular biological investigations proved that the Cyclotella genus was not monophyletic. Integrating the above mentioned knowledge the former Cyclotella genus has been split into 4 genera (Cyclotella s.s., Discostella, Tertiarius and Lindavia). Based on the position of rimoportula Lindavia genus was formed for involving the species of both the Cyclotella ocellata and C. bodanica lineages. Our morphological and molecular (genetic distance and phylogenetic analyses of rbcL and 18S rDNA sequences) investigations suggested that "Lindavia/Cyclotella ocellata group" could be raised from the Lindavia as a separate genus. Its distinctive morphological features are the followings: striae unequal in length, central area without areolae. We describe the new genus Pantocsekiella gen. nov. and we transferred several Lindavia taxa into it. We also provide an amended diagnosis for the genus Lindavia

Quantitative Morphometric Analysis of Morphologically Similar Species of <i>Fragilaria</i> (Fragilariaceae, Bacillariophyta) Allows Detection of Non-Indigenous Taxa: A Case Study from Lake Ladoga (North of European Russia)

In Lake Ladoga (northwestern Russia), we found a diatom, putatively Fragilaria sublanceolata-baikali, an endemic species from Lake Baikal (southeastern Siberia, Russia). To determine whether this population matches a previously recognized species from Lake Baikal and assess how it differs from other similar Fragilaria taxa, we studied the valve morphology of three morphologically similar Fragilaria populations (the putative F. sublanceolata-baikali, F. pectinalis and F. perminuta) sampled in Lake Ladoga, along with a population of F. sublanceolata-baikali sampled in Lake Baikal. We used light and scanning electron microscopy with a combination of traditional and geometric morphometric methods. To analyze covariation between the valve shape and size (i.e., allometry), we examined differences in the ontogenetic–allometric trajectories at both the interspecific and intraspecific levels. In addition, the effect of size correction of the valve shape on species differentiation was tested. Traditional morphometrics revealed that F. sublanceolata-baikali is distinguished from F. pectinalis and F. perminuta by valve length, while F. pectinalis and F. perminuta are distinguished by striae density. All three species of Fragilaria showed separate and parallel allometric trajectories. In contrast, the two populations of F. sublanceolata-baikali were on a common allometric trajectory, indicating the conspecificity between these populations. Prior to allometric correction, geometric morphometrics was not able fully discriminate between the three Fragilaria species. After allometric correction, the three Fragilaria species were clearly separated in a size-corrected morphospace, whereas the two populations of F. sublanceolata-baikali formed a tightly overlapping group. Thus, we conclude that geometric morphometrics can reliably distinguish between these morphologically similar species of Fragilaria, but only after accounting for allometric shape variation. Our study confirmed morphological similarity between the two geographically distant populations of F. sublanceolata-baikali, which indicates that this taxon can be considered as invasive in Lake Ladoga

Halamphora taxa in Hungarian soda pans and shallow soda lakes detected via metabarcoding and microscopic analyses

The research presented investigates whether DNA-based metabarcoding can replace the morphology-based identification of diatom taxa in the ecological status assessments of aquatic habitats. When comparing data obtained with microscopy and metabarcoding, significant deviations have been noticed. One of the main reasons includes the incompleteness of the reference database used for taxonomic annotation of sequences. The database library should be complemented with species inhabiting unique habitats and having specific environmental requirements representing environmental endpoints for genetic diversification. Soda pans and soda lakes are examples of an extreme habitat with the loss of sodic character as the main threat; thus, accurate identification of species and exact information on their salinity tolerance is essential for adequate ecological status assessment. In the present study, by using microscopy and metabarcoding, we investigated taxa of the genus Halamphora that are common in soda pans and soda lakes. We detected six species of which Halamphora dominici and H. veneta occurred frequently and often in high abundance (it was often dominant having relative abundance higher than 5%). Analyses of DNA data confirmed the separation of the two species; as a result, the reference database library has been supplemented with sequences of H. dominici. Furthermore, we have confirmed that this species, which is a significant indicator of sodic character, shows a positive correlation with salinity

Use of Self-Organizing Maps (SOM) for characterization of riverrine phytoplankton associations in Hungary

The phytoplankton database of the Middle Danube Basin was analysed and evaluated in order to describe the characteristic algal assemblages of the rivers. The dataset were extracted from the database of the Hungarian monitoring network and academic institutions. We implemented the Kohonen Self Organizing Map (SOM) method by which we can visualize the assemblages in topology-preserving projection of two-dimensional space. The method is capable of evaluating large datasets (more than 1800 samples in the present investigation). As a result, we can identify the different algal communities which characterize different river types. The algal communities were described as different ratios of algal functional groups. Since some of the groups are in close relation with certain types of environmental pressure it is also possible to highlight those rivers or river sections (or those periods) which are far from the expected good ecological status